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  1. Pathologic mechanisms
    1. immune mediated diseases in which binding of circulating antibodies to specialized regions at the nodes of Ranvier causes a block of electrical conduction and damage of adjacent axons or myelin
    2. toxic or metabolic agents that attack Schwann cells
      1. diphtheria is a bacterial toxin that acts directly on the membranes of the Schwann cells near the dorsal root ganglia and adjacent parts of motor and sensory nerves; destroys the myelin sheath
        1. Remember: you can buy a ‘dip’ of ice cream from the Schwann salesman
      2. polyarteritis nodosa causes widespread occlusion of the vasa nervosum causing destruction of axon and myelin
      3. Guillan Barre – endoneurial infiltration of lymphocytes, plasma cells, and other mononuclear cells in the roots, sensory and sympathetic ganglia, and nerves
  2. recovery of function may be rapid because denuded axons only need to be remyelinated; the newly formed internodal segments are thinner than normal and of variable length (by contrast Wallerian or axonal regeneration is slower requiring months to regenerate)
    1. when the regenerating axon becomes remyelinated, the internodal segments are inappropriately short, one old internode being replaced by 3-4 new ones; recurrent demyleination and remyelination leads to onion bulb formations
    2. demyelination may be seen histopathologically with stains for myelin including Weiger, Marchi, and Sudan stains
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